How can I create procedural tiles with uniquely seeded textures for each one? [Updated]
I wonder how much computational difference there actually is,between using the Voronoi node for tiling, and doing the maths yourself, especially after you've introduced a couple of Noise nodes to do your randomness for you.. ?
Anyway, you certainly get lot out for not much in, in the way of nodes, with this kind of tree..

(I've made a group of it, here) .. You get UV-per-Cell, by subtracting the Position output from the texture-space, which lets you tile any texture you like into each cell:

You get 3 random numbers (a color) per cell, which you can use to randomise any of the cell's attributes (here, used to randomly rotate a texture, per cell):

And from the parallel Voronoi in the tree, you can get the distance to the cell's edges, which you can use to make a grouting mask, as here, or you can map ranges of it to other ranges to bevel tile edges:

And you can use the Randomness setting in the Voronoi nodes to take you from square tiles..

.. to Voronoi tiles, without any further adjustment.


(Just the group.. the other trees are a bit of a rushed mess :) )